1. Field of the Invention
This invention relates to a current to frequency converter having an operational amplifier and level detector therein, and more particularly, this invention relates to a current to frequency converter having an operational amplifier which has its non-inverting input connected to a constant voltage and its output disabled when a level detector, which is connected to the output of the operational amplifier, detects a predetermined voltage level until the output of the operational amplifier reaches a second predetermined voltage level.
2. Description of the Prior Art
The voltage to frequency converter generally known as VFC32 produced by Burr-Brown has a resistor between its voltage input and the negative input of its operational amplifier. Also connected to the negative input of the operational amplifier is a capacitor, which has its other opposite side connected to the output of the operational amplifier. The negative input of the operational amplifier is also connected to a constant current sink through switch. The switch which is normally open is capable of selectively providing an open circuit or alternately actuating the constant current sink. The output of the operational amplifier is connected to the negative input of a comparator. The positive input of the comparator is connected to ground, as is the positive input of the operational amplifier. The output of the comparator is connected to the input of a one-shot device. The output of the one-shot device is connected in a manner to close the switch when the one-shot device is actuated and through a transistor to provide a pulse of known duration when the output of the comparator indicates that the output of the operational amplifier is at ground or close thereto. In operation, when the switch is closed, the output of the operational amplifier increases to a predetermined value. The switch is then opened and the output of the operational amplifier responding to the voltage applied to the input to the voltage to frequency converter reduces from the predetermined value at a rate proportional to the voltage level at the input. When the voltage level is close to zero, the comparator so indicates to the one-shot device which produces a pulse which in turn closes the switch to ground. The constant current sink, which is attached to the negative input of the amplifier, causes the output of the input amplifier to increase until it reaches the predetermined value. Thus, the frequency of the pulses produced at the output of the one-shot device is proportional to the voltage level present at the input to the voltage to frequency converter.